I've run into some difficulty with my chemistry homework. We went over this practise question in class today as an example. However, I wasn't able to fully grasp how to work it out.

Question

"How many grams of nitrogen form when 34.6 grams of nitrogen dioxide decomposes according to this
chemical equation:2 NO2 --> N2 + 2 O2?"

Answer 1

Kara,

the conceptual plan would be to go from grams of No2 to grams of N2 by first using the molar mass to convert grams to moles of NO2. Now use the mole ratio of NO2 to N2, then use the Molar mass of N2 to get grams of N2

Answer 2

Work from mole:mole ratios. That is, convert given grams of NO to moles and apply to equation.

Let x = moles of N2 produced and set up a linear ratio;i.e,
From the equation, 2NO => N2 + 2O2 => (2 mole NO/1.153 mole NO) = (1 mole N2/x) Solve for 'x'= (1/2)(1.153 mole N2) = 0.577 mole N2 Theoretical Yield. If you need gram yield, multiply mole Yield of N2 by formula wt of N2 (=28g/mole). That is, gms N2 = (0.577 mole N2)(28g/mole) = 16.14gms N2.

Let y = moles of O2 produced and set up linear ratio as before...
=> (2 mole NO2/ 1.153 mole NO2) = (2 mole O2/y) and solve for y = 1.153 mole O2 Theoretical Yield. For grams O2, multiply Theoretical Yield by 32g/mole. That is, gms O2 = (1.153 mole O2)(32 gms/mole) = 36.896 gms O2. Note, since coefficients in the equation for NO and O2 are the same, you can assume that 1.153 mole of O2 will be obtained from 1.153 mole of NO. N2 is half of equation moles NO.